title: Hyperexcitability of parietal-motor functional connections in the intact left-hemisphere of patients with neglect.
abstract: Hemispatial neglect is common after unilateral brain damage, particularly to perisylvian structures in the right-hemisphere (RH). In this disabling syndrome, behaviour and awareness are biased away from the contralesional side of space towards the ipsilesional side. Theoretical accounts of this in terms of hemispheric rivalry have speculated that the intact left-hemisphere (LH) may become hyper-excitable after a RH lesion, due to release of inhibition from the damaged hemisphere. We tested this directly using a novel twin-coil transcranial magnetic stimulation (TMS) approach to measure excitability within the intact LH of neglect patients. This involved applying a conditioning TMS pulse over left posterior parietal cortex (PPC), in order to test its effect on the amplitude of motor evoked potentials (MEPs) produced by a subsequent test pulse over left motor cortex (M1). Twelve RH stroke patients with neglect, an age-matched group of eight RH stroke patients without neglect, and 10 healthy controls were examined. We found that excitability of left PPC-M1 circuits was higher in neglect patients than the other groups, and related to the degree of neglect on clinical cancellation tests. A follow-up found that 1 Hz repetitive TMS over left PPC normalized this over-excitability, and also ameliorated visual neglect on an experimental measure with chimeric objects. Our results provide 'direct' evidence for pathological over-excitability of the LH in the neglect syndrome, as quantified by left PPC influences on left M1, with implications for possible treatment.
authors.affiliation: Laboratorio di Neurologia Clinica e Comportamentale, Fondazione Santa Lucia IRCCS, Rome, Italy. g.koch@hsantalucia.it
authors.forename: Giacomo
authors.initials: G
authors.lastname: Koch
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Oliveri
authors.forename: Binith
authors.initials: B
authors.lastname: Cheeran
authors.forename: Diane
authors.initials: D
authors.lastname: Ruge
authors.forename: Emanuele
authors.initials: E
authors.lastname: Lo Gerfo
authors.forename: Silvia
authors.initials: S
authors.lastname: Salerno
authors.forename: Sara
authors.initials: S
authors.lastname: Torriero
authors.forename: Barbara
authors.initials: B
authors.lastname: Marconi
authors.forename: Francesco
authors.initials: F
authors.lastname: Mori
authors.forename: Jon
authors.initials: J
authors.lastname: Driver
authors.forename: John C
authors.initials: JC
authors.lastname: Rothwell
authors.forename: Carlo
authors.initials: C
authors.lastname: Caltagirone
mesh_terms: D000328:Adult; D000368:Aged; D019054:Evoked Potentials, Motor; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology*; D009434:Neural Pathways / Q000503:physiopathology; D010296:Parietal Lobe / Q000503:physiopathology*; D010468:Perceptual Disorders / Q000209:etiology / Q000503:physiopathology*; D011597:Psychomotor Performance; D020521:Stroke / Q000473:pathology / Q000503:physiopathology / Q000523:psychology; D050781:Transcranial Magnetic Stimulation / Q000379:methods